Laser-processable glass substrate and laser processing method

ABSTRACT

A sheet of silicate glass having a thickness of 2 mm and composed mainly of SiO2, and containing Al2O3, B2O3, Na2O, F, etc., is immersed in a molten salt comprising a mixture of 50 mol % of silver nitrate and 50 mol % of sodium nitrate. Na ions in the surface of the glass are eluted, diffusing Ag ions in the molten salt into the glass. When a laser beam is applied to the glass substrate thus formed, the glass substrate is evaporated or ablated progressively from its surface. The glass substrate is processed to a smooth finish without causing cracking or breakage.

TECHNICAL FIELD

The present invention relates to a glass substrate suitable for beingprocessed by laser, and a method of processing such a glass substrate.

BACKGROUND ART

Laser beams have an intensive energy, and have heretofore been used toincrease the temperature of a surface of a material to which the laserbeam is applied thereby to ablate or evaporate a portion of the materialto which the laser beam is applied, for processing the material invarious ways. Since the laser beam can be focused into a very smallspot, it is suitable for microscopic topographic processing of amaterial.

Laser beams are generated by an infrared laser such as a CO₂ laser, anNd:YAG laser, a laser comprising an Nd:YAG laser combined with awavelength conversion capability for producing a laser beam whosewavelength ranges from a near-infrared region through a visible regionto an ultraviolet region, and an ultraviolet laser such as an excimerlaser such as an Arf or Krf laser.

Silicate glass composed primarily of SiO₂ is highly transparent and caneasily be molded (deformed) at high temperatures. Sheets of silicateglass, which have been formed with holes or concavities and convexitiesby microscopic topographic processing, are widely used as glasssubstrates for optical components used for optical communications anddisplay devices.

In order to make a hole in a sheet of silicate glass according tomicroscopic topographic processing, it has been the general practice toprocess the sheet of silicate glass with wet etching (chemical etching)using an etchant of hydrofluoric acid or the like, or dry etching(physical etching) such as reactive ion etching.

However, the wet etching suffers problems with respect to management andprocessing of the etchant. The dry etching requires pieces of equipmentsuch as a vacuum container, needs a large-scale apparatus, and is notefficient because a pattern mask has to be produced by complexphotolithography.

It has been attempted to use a laser beam for microscopic topographicprocessing of glass. Since glass is fragile, it tends to crack whenprocessed. If an infrared carbon dioxide laser is used to process glass,the glass will violently crack due to thermal strain.

If an ultraviolet KrF excimer laser (wavelength of 248 nm) is used toprocess glass, the glass will crack around the area where the laser beamis applied. The ultraviolet KrF excimer laser (wavelength of 248 nm) isthus not suitable for microscopic topographic processing of glass. Theuse of an ArF excimer laser having a wavelength of 193 nm for emitting alaser beam to process glass is optimum. However, even when such an ArFexcimer laser is used, the generation of microcracks is unavoidable.

The ArF excimer laser having a wavelength of 193 nm is subject toabsorption by air, and needs to replace the transmission medium with anabsorption-free gas such as Ar or a vacuum in order to allow the laserbeam to reach as far away as possible.

There has been proposed a technique disclosed in Japanese laid-openpatent publication No.54-28590. According to the disclosed technique,when a laser beam is applied to process a glass substrate, the glasssubstrate has been heated to 300˜700° C. in advance to withstand thermalshocks caused when it is processed with the laser beam.

When the glass substrate is subject to microscopic topographicprocessing by the laser beam while it is being heated to relax stresses,however, the glass substrate cannot be processed to an accuracy rangingfrom micrometers to submicrometers because of thermal shrinkage.

Even when the glass substrate is subject to microscopic topographicprocessing by the laser beam while it is being heated, the processedarea has a rough surface, but not a smooth finish. The processed glasssubstrate is still susceptible to cracking or breakage.

The inventors have attempted to apply a laser beam to generalphotosensitive glass which contains a uniform concentration of Ag ions.The process of applying the laser beam to the general photosensitiveglass will be described below with reference to FIGS. 1(a) 1(d) of theaccompanying drawings. As shown in FIG. 1 (a), a laser beam applied to aglass substrate enters into the glass substrate, reducing Ag ionspresent in the glass substrate as shown in FIG. 1(b) thereby to generatea colloid (very fine particles of Ag). When the colloid is separatedout, as shown in FIG. 1(c), the coefficient of absorption of the laserbeam is greatly increased. The glass substrate now starts being ablatedfrom inside thereof until finally it develops a recess-like crack orbreakage as shown in FIG. 1(d).

DISCLOSURE OF THE INVENTION

The present invention has been made in an attempt to eliminate the aboveconventional drawbacks. It is an object of the present invention toprovide a glass substrate which is capable of relaxing thermal stresses,does not develop cracking and breakage, and produces a smooth processedarea when a hole or a concavity and a convexity are formed in the glasssubstrate by laser processing.

Another object of the present invention is to form a microscopic patternof concavities and convexities on the glass substrate described abovewith a laser beam.

A laser-processable glass substrate according to the present inventioncontains silver in the form of Ag atoms, an Ag colloid, or Ag ions froma surface thereof to a predetermined depth and has such a concentrationgradient that the concentration of silver is greatest at the surface andprogressively decreases from the surface to the predetermined depth.

Another laser-processable glass substrate according to the presentinvention contains silver throughout its entirety and has such aconcentration gradient that the concentration of silver is greatest at asurface thereof and progressively decreases from the surface to anopposite surface.

Still another laser-processable glass substrate according to the presentinvention contains silver throughout its entirety and has such aconcentration gradient that the concentration of silver is smallest(including a concentration of 0 mol %) at an intermediate region in adirection transversely across the glass substrate and progressivelyincreases toward opposite surfaces thereof.

The laser-processable glass substrate may be of a planar shape or acylindrical shape or any of other desired shapes. The laser-processableglass substrate should preferably comprise silicate glass composedprimarily of SiO₂ for its high transparency.

The laser-processable glass substrate should preferably contain F(fluorine) in order to reduce coloring due to Ag ions.

For introducing silver into glass to achieve a concentration gradient,Ag ions replace one-valence positive ions other than Ag ions by way ofan ion exchange.

If the concentration of silver were low, the absorbed energy of thelaser beam would also be low, making the glass substrate to be lesssusceptible to evaporation or ablation. For this reason, theconcentration of silver in an area where the glass substrate is to beprocessed should preferably be at least 0.1 mol %.

In order to form a through hole or a recess in the laser-processableglass substrate, a laser beam is applied to the surface thereof wherethe concentration of silver is greatest, as shown in FIG. 2(a) of theaccompanying drawings. Then, as shown in FIG. 2(b) of the accompanyingdrawings, silver (Ag ions) in the surface where the concentration ofsilver is greatest are reduced into a colloid (very fine particles ofAg). The colloid absorbs the energy of the laser beam, which causes theglass to be melted, evaporated, or ablated to remove a surface layer ofthe glass, as shown in FIG. 2(c) of the accompanying drawings. When thesurface layer is removed, a lower layer of the glass is then similarlyremoved. Finally, a recess or a through hole is formed as shown in FIG.2(d) of the accompanying drawings.

A laser beam may be applied to a surface of the glass substrate which isopposite to the surface thereof where the concentration of silver isgreatest, as shown in FIG. 3(a) of the accompanying drawings. Then, asshown in FIGS. 3(b)˜3(d) of the accompanying drawings, silver (Ag ions)in the surface where the concentration of silver is greatest are reducedinto a colloid (very fine particles of Ag) The colloid absorbs theenergy of the laser beam, which causes the glass to be melted,evaporated, or ablated to remove a surface layer of the glass. When thesurface layer is removed, a lower layer of the glass is then similarlyremoved. Finally, a recess or a through hole is formed.

The colloid of silver may be formed by applying ultraviolet radiationrather than the laser beam. Since no ablation or the like can be broughtabout by ultraviolet radiation, however, a laser beam is applied to forma hole or the like in the glass substrate after ultraviolet radiation isapplied.

A colloid may be separated out by heating the glass substrate ratherthan applying ultraviolet radiation or a laser beam.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a)˜(d) are diagrams showing a process of applying a laser beamto photosensitive glass which contains a uniform concentration of Agions;

FIGS. 2(a)˜2(d) are diagrams showing a process of applying a laser beamto a laser-processable glass substrate according to the presentinvention;

FIGS. 3(a)˜3(d) are diagrams similar to FIGS. 2(a)˜2(d) except that alaser beam is applied in a different direction;

FIG. 4 is a schematic view of a device used for an ion exchange;

FIG. 5(a) is a photographic representation of a recess formed in theglass substrate according to the present invention, as observed using amicroscope;

FIG. 5(b) is a diagram produced on the basis of the photographicrepresentation shown in FIG. 5(a);

FIG. 6 is a graph showing the recess measured using a surface roughnessmeasuring unit with a stylus;

FIG. 7(a) is a photographic representation of a recess formed in a glasssubstrate which has not been subjected to an ion exchange, as observedusing a microscope;

FIG. 7(b) is a diagram produced on the basis of the photographicrepresentation shown in FIG. 7(a);

FIG. 8 is a graph showing the relationship between the depths ofrecesses processed by a laser beam and the energy of the laser beamapplied;

FIG. 9 is a view of a specific product which has been produced byprocessing the glass substrate according to the present invention with alaser beam; and

FIG. 10 is a view of another shape of glass substrate according to thepresent invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Examples of the present invention will be described below with referenceto the accompanying drawings and Tables. Table 1 shows ion exchangeconditions, laser beam applying conditions, and laser processability ofInventive Examples. Table 2 shows ion exchange conditions, laser beamapplying conditions, and laser processability of Comparative Examples.Table 3 shows specific compositions of glass substrates.

When a glass substrate has laser processability, it means that the glasssubstrate is free from cracking and breakage and the area of the glasssubstrate where a laser beam is applied is smooth.

TABLE 1 Ion exchange conditions Laser Salt concentra- Applying proces-In. Ex. Glass tion Time Annealing conditions sability In. Ex. 1 A ofTable 3 Silver nitrate: 300° C. 15 None YAG355 nm ∘ min. 50 mol %, 6hrs. ″ YAG355 nm ∘ Sodium nitrate: 86 hrs. ″ YAG355 nm ∘ 50 mol % In.Ex. 2 B of Table 3 Silver nitrate: 280° C. 1 hr. ″ YAG355 nm ∘ 100 mol %In. Ex. 3 C of Table 3 Same as In. Ex. 1 300° C. ″ YAG355 nm ∘ 6 hrs. ″YAG355 nm ∘ 86 hrs. ″ YAG355 nm ∘ In. Ex. 4 D of Table 3 Same as In Ex.1 300° C. 30 ″ YAG355 nm ∘ min. In. Ex. 5 E of Table 3 Same as In. Ex. 2300° C. 30 ″ YAG355 nm ∘ min. In. Ex. 6 C of Table 3 Same as In. Ex. 2300° C. 15 ″ YAG355 nm ∘ min. In. Ex. 7 A of Table 3 Same as In. Ex. 2300° C. 15 350° C. 3 hrs. YAG355 nm ∘ min. 350° C. 6 hrs. In. Ex. 8 A ofTable 3 Same as In. Ex. 2 300° C. 10 350° C. 6 hrs. YAG355 nm Δ sec.

TABLE 2 Laser Ion ex- Applying proces- Comparative Ex. Glass changeconditions ability Comparative Ex. 1 A of Table 3 None YAG248 nm xComparative Ex. 2 B of Table 3 ″ YAG355 nm x Comparative Ex. 3 C ofTable 3 ″ YAG355 nm x Comparative Ex. 4 D of Table 3 ″ YAG355 nm xComparative Ex. 5 E of Table 3 ″ YAG355 nm x Comparative Ex. 6 C ofTable 3 ″ YAG532 nm x Comparative Ex. 7 Antifungal glass ″ YAG355 nm xComparative Ex. 8 A of Table 3 * YAG355 nm x *After Ag′ is introduced byway of an ion exchange, Ag′ in the surface is converted into Na by wayof an ion exchange.

TABLE 3 Comp. Glass SiO₂ Al₂O₃ B₂O₃ ZnO MgO CaO Na₂O K₂O F— Ag₂O Fe₂O₃BaO La₂O₃ A 56.0 20.0 11.3 — 0.008 — 11.0 0.002 4.15 0.006 0.008 — — B63.0 — — — — — 27.0 — — — — 7.0 3.0 C 66.3 2.4 8.6 — 8.7 — 11.0 2.5 — —— — — D 60.1 — 3.5 14.8 — — 13.2 7.7 — — — — — E 71.06 1.47 — — 3.9208.88 13.41 0.820 — — 0.172 — —

INVENTIVE EXAMPLE 1

An ion exchange was conducted using a device shown in FIG. 4. A glasssubstrate (A of Table 3) to be processed was in the form of a sheet ofsilicate glass having a thickness of 2 mm and composed mainly of SiO₂and containing Al₂O₃, B₂O₃, Na₂O, F, etc. A molten salt placed in aquartz container comprised a mixture of 50 mol % of silver nitrate and50 mol % of sodium nitrate.

Specimens of the glass substrate were immersed in the molten salt in thequartz container for 15 minutes, 6 hours, and 86 hours, respectively.The molten salt was kept at 300° C. in an electric furnace, and areactive atmosphere was air.

Na ions (one-valence positive ions) in the surface of the glasssubstrate are eluted, diffusing Ag ions in the molten salt into theglass. The thicknesses of layers into which the Ag ions were diffused,as measured by a microanalyzer, were of about 7 μm for the specimenimmersed for 15 minutes, about 30 μm for the specimen immersed for 6hours, and about 160 μm for the specimen immersed for 86 hours.

Then, a laser beam was applied to the specimens of the glass substrateto remove a certain region thereof by way of evaporation or ablation,trying to produce a recess.

The laser beam was a third harmonic emitted from an Nd:YAG laser andhaving a wavelength of 355 nm. The laser beam had a pulse duration ofabout 10 nsec. and a repetitive frequency of 5 Hz, and was focused by alens before being applied to the glass substrate. The glass had a slightability to absorb the laser beam having a wavelength of 355 nm.

The spot of the applied laser beam had a size of 360 μm. The energy Ofthe applied laser beam was 39 J/cm². The laser beam was applied in 30shots. After the application of the laser beam, a recess having a depthof about 10 μm was formed in the surface of the glass substrate.

FIG. 5(a) is a photographic representation of the recess thus formed inthe glass substrate, FIG. 5(b) is a diagram produced on the basis of thephotographic representation shown in FIG. 5(a), and FIG. 6 is a graphshowing the area where the laser beam was applied, measured using asurface roughness measuring unit with a stylus. It can be seen fromthese figures that there is not cracking or breakage at all around thespot where the laser beam was applied, and the area where the laser beamwas applied was smooth, resulting in a smooth profile.

A laser beam was applied under the same conditions to a glass which wasnot subjected to an ion exchange. FIG. 7(a) is a photographicrepresentation of the recess formed in the glass, and FIG. 7(b) is adiagram produced on the basis of the photographic representation shownin FIG. 7(a). As can be seen from these figures, the glass substrate wasviolently cracked around the area where the laser beam was applied, andthe area where the laser beam was applied had irregular minuteconcavities and convexities and surface irregularities, and did not havea smooth surface. The irregular concavities and convexities were solarge that the surface roughness could not be measured by a surfaceroughness measuring unit with a stylus.

As described above, the surface which was subjected to an ion exchangewas given good processability, and the good processability did notdepend on the time required by the ion exchange.

When the laser beam was continuously applied to the glass substratewhich was subjected to an ion exchange for 15 minutes, the area to whichthe laser beam was applied was roughened, losing its laserprocessability.

The specimens were experimented with the energy of the applied laserbeam being changed by changing the position where the laser beam wasfocused. As a result, it was found that those specimens which weresubjected to an ion exchange exhibited good results. The laser beam wasapplied in 30 shots, and the depths of formed recesses were measured bya surface roughness measuring unit with a stylus for their dependency onthe energy of the applied laser beam. As shown in FIG. 8, there is agood linearity between the depths of the formed recesses and the energyof the applied laser beam, allowing adjustments to be easily made by theenergy of the applied laser beam which is an important quantity forlaser processability.

COMPARATIVE EXAMPLE 1

A laser beam produced by an excimer laser having a wavelength of 248 nmwas applied to form a recess in a glass substrate which was of the samecomposition as the glass substrate in Inventive Example 1 and was notsubjected to an ion exchange. As a result, the glass substrate developedcracking and breakage, and no laser processability was observed.

INVENTIVE EXAMPLE 2

An ion exchange was conducted using the device shown in FIG. 4. A glasssubstrate (B of Table 3) to be processed was in the form of a sheet ofsilicate glass having a thickness of 2 mm and mainly composed of SiO₂and containing B₂O₃, Na₂O, etc. As shown in Table 1, the molten saltplaced in a quartz container comprised only silver nitrate. The reactiveatmosphere was air, and the glass substrate was immersed in the moltensalt at 280° C. for 1 hour.

A laser beam emitted from a YAG laser having a wavelength of 355 nm wasapplied at an energy of 30 j/cm² to the glass substrate which wassubjected to an ion exchange as shown in Table 1.

As a result, the glass substrate which was subjected to an ion exchangeexhibited laser processability. When the distribution of Ag ions wasmeasured by an X-ray microanalyzer, almost all Ag ions on the glasssurface were exchanged, and their concentration was 27 mol %.

COMPARATIVE EXAMPLE 2

A laser beam produced by a YAG laser having a wavelength of 355 nm wasapplied at an energy of 30 j/cm² to a glass substrate which was of shesame composition as the glass substrate in Inventive Example 2 and wasnot subjected to an ion exchange. As a result, the glass substratedeveloped cracking and breakage, and no laser processability wasobserved.

INVENTIVE EXAMPLE 3

A glass substrate to be processed had a composition of C of Table 3, andwas subjected to an ion exchange under the same conditions as those ofInventive Example 1. A laser beam was applied to the glass substrateunder the same applying conditions as those of Inventive Example 1 tocheck the glass substrate for laser processability. As a result, theglass substrate which was subjected to an ion exchange exhibited laserprocessability.

COMPARATIVE EXAMPLE 3

A laser beam produced by a YAG laser was applied under the sameconditions as those of Inventive Example 3 to a glass substrate whichhad the same composition as the glass substrate in Inventive Example 3and was not subjected to an ion exchange. As a result, the glasssubstrate developed cracking and breakage, and no laser processabilitywas observed.

INVENTIVE EXAMPLE 4

A glass substrate to be processed had a composition of D of Table 3, andwas subjected to an ion exchange with the same molten salt as that usedin Inventive Example 1 for 30 minutes at 300° C. A laser beam wasapplied Lo the glass substrate under the same applying conditions asthose of Inventive Example 1 to check the glass substrate for laserprocessability. As a result, the glass substrate which was subjected toan ion exchange exhibited laser processability.

COMPARATIVE EXAMPLE 4

A laser beam produced by a YAG laser was applied under the sameconditions as those of Inventive Example 4 to a glass substrate whichhad the same composition as the glass substrate in Inventive Example 4and was not subjected to an ion exchange. As a result, the glasssubstrate developed cracking and breakage, and no laser processabilitywas observed.

INVENTIVE EXAMPLE 5

A glass substrate to be processed had a composition of E of Table 3, andwas subjected to an ion exchange with the same molten salt as that usedin Inventive Example 1 for 30 minutes at 300° C. A laser beam wasapplied to the glass substrate under the same applying conditions asthose of Inventive Example 1 to check the glass substrate for laserprocessability. As a result, the glass substrate which was subjected toan ion exchange exhibited laser processability.

COMPARATIVE EXAMPLE 5

A laser beam produced by a YAG laser was applied under the sameconditions as those of Inventive Example 5 to a glass substrate whichhad the same composition as the glass substrate in Inventive Example 5and was not subjected to an ion exchange. As a result, the glasssubstrate developed cracking and breakage, and no laser processabilitywas observed.

INVENTIVE EXAMPLE 6

A glass substrate to be processed had a composition of C of Table 3, andwas subjected to an ion exchange with the same molten salt as that usedin Inventive Example 1 for 15 minutes at 300° C. A laser beam emitted bya YAG laser having a wavelength of 532 nm was applied to the glasssubstrate to check the glass substrate for laser processability. As aresult, the glass substrate which was subjected to an ion exchangeexhibited laser processability.

COMPARATIVE EXAMPLE 6

A laser beam produced by a YAG laser was applied under the sameconditions as those of Inventive Example 6 to a glass substrate whichhad the same composition as the glass substrate in Inventive Example 6and was not subjected to an ion exchange. As a result, the glasssubstrate developed cracking and breakage, and no laser processabilitywas observed.

INVENTIVE EXAMPLE 7

Specimens of a glass substrate to be processed which was subjected to anion exchange for 15 minutes under the same conditions as those ofInventive Example 1 were annealed under different conditions, i.e., at350° C. for 3 hours and at 350° C. for 6 hours. As a result, theconcentration of silver, which was 2.57 mol % prior to annealing, wasreduced to 0.63 mol % for the specimen that was annealed at 350° C. for3 hours, and to 0.49 mol % for the specimen that was annealed at 350° C.for 6 hours.

A laser beam emitted from a YAG laser having a wavelength of 355 nm wasapplied to the annealed specimens at an energy of 40 mJ/pulse, with apulse duration of about 10 nsec. at a repetitive frequency of 5 Hz.

As a result, laser processability was confirmed for all the specimens.However, the ablation threshold (the energy density at which ablationstarts to occur) increased by 4˜5 times from the ablation threshold of aglass substrate which was not annealed.

INVENTIVE EXAMPLE 8

Specimens of a glass substrate to be processed were subjected to an ionexchange under the same conditions as those of Inventive Example 1except that the ion exchange was conducted for a short time of 10seconds, and then annealed at 350° C. for 6 hours. As a result, theconcentration of silver in the surface of the specimens was reduced to0.06 mol %. A laser beam was applied to the specimens under the sameconditions as those of Inventive Example 7.

As a result, some of the specimens, exhibited laser processability, butthe other specimens developed cracking and breakage.

As can be seen from Inventive Examples 7 and 8 described above, thosespecimens which have a concentration gradient of silver exhibit laserprocessability even though the concentration of silver is low, and thelower limit of silver concentration for which laser processability wasconfirmed is 0.06 mol %. Not all specimens, but 20˜30% thereof, exhibitlaser processability. For a glass substrate to exhibit reliable laserprocessability, the concentration of silver thereof needs to be of 0.1mol % or higher.

COMPARATIVE EXAMPLE 7

A laser beam emitted from a YAG laser having a wavelength of 355 nm wasapplied to antifungal glass with a uniform content of silver (SiO₂: 37.5mol %, B₂O₃: 46.5 mol %, Na₂O: 15.8 mol %, Ag₂O: 0.28 mol %) at anenergy of 88 mJ/pulse, with a pulse duration of about 10 nsec. at arepetitive frequency of 5 Hz. As a result, the area to which the laserbeam was applied was rendered rough with cracking observed around thearea.

COMPARATIVE EXAMPLE 8

A glass substrate to be processed was fabricated which had a lowconcentration of silver in the surface and a concentration gradient withthe silver concentration progressively increasing from the surface intothe glass substrate. The glass substrate was fabricated by immersing ablank glass substrate in a molten salt composed of a mixture of 50 mol %of silver nitrate and 50 mol % of sodium nitrate, for 60 minutes, sothat the glass substrate had a concentration gradient with the silverconcentration being greatest at the surface and progressively decreasingaway from the surface, as with Inventive Example 1. The glass substratewas then immersed in a molten salt composed of 62.5 mol % of sodiumnitrite and 37.5 mol % of sodium nitrate, for 20 minutes, replacing Agions in the surface again with Na ions. As a result, the glass substratehad a lowered silver concentration in the surface with the silverconcentration being greatest in a intermediate region in a directiontransversely across the glass substrate.

A laser beam emitted from a YAG laser having a wavelength of 355 nm wasapplied to the glass substrate at an energy of 40 mJ/pulse, with a pulseduration of about 10 nsec. at a repetitive frequency of 5 Hz. As aresult, the area to which the laser beam was applied was rendered roughwith cracking observed around the area.

The same results were obtained when the glass substrate was immersedfirst in silver nitrate and sodium nitrate for 15 minutes and then insodium nitrate for 120 minutes.

It can be understood prom Comparative Examples 7 and 8 described abovethat a glass substrate does not exhibit laser processability if itsimply contains silver or has a high silver concentration at its center,and a glass substrate is required to have a silver concentration whichis greatest at its surface and progressively decreases away from thesurface in order to exhibit laser processability.

FIG. 9 shows a specific product which has been produced by processingthe glass substrate according to the present invention with a laserbeam. The product comprises a glass substrate G mounted on a siliconbase W, the glass substrate G having a composition according to thepresent invention. A through hole h is formed into the glass substrate Gby laser processing, and a conductive body d is disposed in the throughhole h for electrically connecting a circuit formed on the glasssubstrate G and the silicon base W.

A glass substrate with through holes formed therein may be incorporatedin an ink jet head, and a glass substrate with recesses formed thereinmaybe incorporated in a microlens array or the like.

The glass substrate is not limited to a planar shape, but may be of acylindrical or prismatic shape. If the glass substrate is of acylindrical or prismatic shape, then it has such a concentrationgradient that the silver concentration is greatest at its outer surfaceand progressively decreases toward the center of the glass substrate.

As described above, the laser-processable glass substrate according tothe present invention contains silver in the form of Ag atoms, an Agcolloid, or Ag ions from a surface thereof to a predetermined depth andhas such a concentration gradient that the concentration of silver isgreatest at the surface and progressively decreases from the surface tothe predetermined depth, or contains silver throughout its entirety andhas such a concentration gradient that the concentration of silver isgreatest at a surface thereof and progressively decreases from thesurface to an opposite surface, or contains silver throughout itsentirety and has such a concentration gradient that the concentration ofsilver is smallest at an intermediate region in a direction transverselyacross the glass substrate and progressively increases toward oppositesurfaces thereof. When a hole or a concavity and a convexity are formedin the glass substrate by a laser beam, the glass substrate is capableof relaxing thermal stresses, does not develop cracking and breakage,and produces a smooth processed area. Therefore, the glass substrate issuitable for being processed by a laser beam to form a microscopictopographic pattern of concavities and convexities, draw an image on itssurface, or form microscopic holes therein.

When the glass substrate is subjected to microscopic laser processing,the glass substrate does not lose its inherent transparency andinsulation, a heating device and a vacuum container are not required,and the glass substrate can be processed microscopically at roomtemperature.

INDUSTRIAL APPLICABILITY

A glass substrate and a method of processing the glass substrate with alaser beam are contributable to the fabrication of an optical productsuch as a planar microlens array or the like.

We claim:
 1. Method of producing a glass article having at least onehole (h) or a recess, respectively, at a predetermined location in thesurface thereof, characterized by the steps of providing a glasssubstrate (G) containing silver in the form of Ag atoms, an Ag colloid,or Ag ions, and having such a concentration gradient that theconcentration of silver is greatest at said surface and progressivelydecreases from the surface towards the interior, and forming said atleast one hole (h) or recess by irradiating said glass substrate (G) atsaid predetermined location with a laser beam, thereby to removeportions of said glass substrate (G) by way of melting, evaporation orablation due to absorption of energy of said laser beam.
 2. Method ofproducing a glass article according to claim 1, characterized by thestep of applying ultraviolet radiation to the glass substrate to reduceAg ions in the glass substrate into a colloid prior to applying saidlaser beam to said predetermined location.
 3. Method of producing aglass article according to claim 1, characterized in that the silvercontent of said glass substrate is locally restricted to a predetermineddepth from the surface towards the interior of said glass substrate. 4.Method of producing a glass article according to claim 1, characterizedin that said glass substrate contains silver throughout its entirety andhaving such a concentration gradient that the concentration of silver isgreatest at said surface and progressively decreases from said surfaceto an opposite surface.
 5. Method of producing a glass article accordingto claim 1, characterized in that said glass substrate contains silverthroughout its entirety and having such a concentration gradient thatthe concentration of silver is smallest at an intermediate region in adirection transversely across the glass substrate and progressivelyincreases towards opposite surfaces thereof.
 6. Method of producing aglass article according to claim 1, characterized in that said glasssubstrate (G) is of planar shape.
 7. Method according to claim 1characterized in that said glass substrate comprises silicate glasscomposed primarily of SiO₂.
 8. Method of producing a glass articleaccording to claim 1, characterized in that said glass substratecontains F (fluorine).
 9. Method of producing a glass article accordingto claim 1, characterized in that the silver is introduced in the glasssubstrate as Ag ions to replace other one-valance positive ions by anion exchange.
 10. Method of producing a glass article according to claim1 wherein the greatest concentration of silver is at least 0.1 mol %.11. Method of producing a glass article according to claim 1,characterized in that said glass substrate is annealed to lessen theconcentration gradient of silver.